What is the right way to do multiple transformation using open3d?

[li-chengyi]

Hi everybody, I have some trouble with the transform method of o3d.geometry.PointCloud:
I found that I get two different outcome when doing multiple transformation using transform method and matrix multiply.
matrix multiply (pcd is a Nx4 matrix):

    pcd = pcd.T
    pcd = np.dot(trans_f2w, np.dot(rot_ff, np.dot(shift_tr, pcd)))
    pcd = pcd.T
    pcd_vector = o3d.geometry.PointCloud()
    pcd_vector.points = o3d.utility.Vector3dVector(pcd[:, :3])

transform method:

    pcd_vector = o3d.geometry.PointCloud()
    pcd_vector.points = o3d.utility.Vector3dVector(pcd[:, :3])
    pcd_vector.transform(shift_tr)
    pcd_vector.transform(rot_ff)
    pcd_vector.transform((trans_f2w))

What is the profound mystery inside transform ?

[ssheorey]

Your two pieces of code should give the same result. Please file a bug report with an example if it doesn't. Transform does left multiplication and each column of x is a homogenous point:

y2 = T2 @ T1 @ x ....

is the same as

pcd_vector.transform(T1)
pcd_vector.transform(T2)

Open3D/cpp/open3d/geometry/Geometry3D.cpp

Line 77 in f8fbef1

void Geometry3D::TransformPoints(const Eigen::Matrix4d& transformation,